Worked Once... Why can't I get it to work anymore?Rated 5 out of 5 stars

This is a great option but it is not working with my FF3.0. When I installed it, it worked fine. After I closed down FF and later reopened it the Close Button was back on each tab and no longer to the right of the tool bar. Now I can get it to work. Tried to uninstall and reinstalling it but nothing. Want to know how to get it to work again.